A scheme of an industrial plant 1 or assembly line, for example for structures or components of motor vehicles, of a known type is represented in FIGS. 1A, 1B, and 1C.
In general, the plant 1 comprises a plurality of processing and/or assembly stations ST, for example cascaded to one another, where each station ST performs a given operation, such as, for example, a machining operation on a piece that it receives at input and/or an assembly of pieces received. For instance, the plant illustrated in FIG. 1A envisages fifteen stations ST, and at the end of the process the last station ST yields the semifinished piece.
In the example considered, the entire plant 1 is divided into control areas A, such as four areas A1, A2, A3 and A4.
As illustrated for example in FIG. 1B, each area A comprises a subset of stations ST controlled by one and the same fixed human-machine-interface (HMI) unit. For instance, the first area A1 may comprise the first four stations ST1, ST2, ST3 and ST4. These stations are monitored and controlled by the first fixed human-machine-interface unit designated by the reference HMI1.
Likewise, the area A2 may comprise the next four stations controlled by the second fixed human-machine-interface unit. In general, the number of stations ST may even be different for the various control areas A.
Consequently, the first station ST1 can receive a piece to be assembled and carry out its pre-set intervention on the original piece for producing a semifinished piece to be supplied at output. The semifinished product at output from the station ST1 is supplied at input to a second station ST2, where it is received and clamped in position for the subsequent process envisaged in the station ST2, etc.
Each station ST is typically equipped with at least one actuator means and/or one sensor means for carrying out and/or monitoring the operations performed in that station. For instance, the operations that are carried out in each station may be: assembly of some additional parts, welding, control of the quality of the welds, etc. There may also be envisaged stations that perform exclusively a function of storage and/or conveyance, such as, for example, the stations ST1, ST6, ST11 and ST15, which may for example be magazines or conveyor belts.
Usually, present in the aforesaid stations ST are one or more industrial robots to render the operation faster and of high quality. An industrial robot is an automatically controlled, re-programmable, multi-purpose manipulator, frequently used in applications of industrial automation for carrying out manufacturing processes. Hence, typically, the actuator means and sensor means are on board said industrial robot and enable execution and monitoring of the various processing steps.
The piece remains in each station ST for the time necessary for carrying out the process or operation established for that given station. At the end of the operation in one station, the piece is released and can proceed along the path towards the next station of the assembly line. For this purpose (see, for example, FIG. 1C), typically each assembly station ST, for example the stations ST2-ST5, ST7-ST10 and ST12-ST14, is equipped with actuator means AT1, AT2, AT3, . . . , for carrying out the process or processes associated to the station and/or with sensor means S1, S2, S3, . . . , for acquisition of parameters on the status of the station.
As mentioned previously, each control area A is typically equipped with a fixed human-machine-interface unit HMI. For instance, the plant illustrated in FIG. 1A envisages four areas A1, A2, A3, and A4, and consequently four fixed human-machine-interface units HMI are provided. Typically, the fixed human-machine-interface unit HMI is provided in an area adjacent to the stations ST that the human-machine interface unit HMI is able to monitor and/or control. In the example illustrated, each fixed human-machine-interface unit HMI monitors and controls the subset of stations of the associated area A.
In particular, to control the stations ST, each fixed human-machine interface HMI is connected through a communication network COM to an electronic control and processing unit PLC, such as, for example, a programmable-logic controller (PLC). For instance, as illustrated in FIG. 1b, the interface HMI1 is connected to the unit PLC1 through a communication network COM1.
The electronic control and processing unit PLC is in turn connected to the stations ST of the associated area A, in particular (see FIG. 1C) to the actuators AT and to the sensors S of the associated stations ST. For instance, for this purpose, a communication network may be used, such as, for example, the network COM1 that is used for communication with the associated interface HMI. For instance, the aforesaid communication network may be an Ethernet, or a CAN (Controller-Area Network) bus, or in general any wired or wireless communication network.
Furthermore, the electronic control and processing unit PLC is connected to a smart terminal of a SCADA (Supervisory Control and Data Acquisition) type that provides for remote monitoring of the entire assembly line. For instance, for this purpose a communication network may be used, such as, for example, the LAN (Local-Area Network), for instance, an Ethernet, preferably wired.
Currently, then, the function of global monitoring lies in the SCADA smart terminal, whereas the local functions of diagnostics, control, and intervention, which are useful in the event of malfunctioning, are managed directly by the fixed human-machine interface HMI set in the vicinity of the assembly stations.
In general, one electronic control and processing unit PLC may also manage the stations of a plurality of areas A and hence interfaces HMI (see, for example, FIG. 2), or vice versa a plurality of electronic control and processing units PLC may be associated to a single area A.
Consequently, in general, the plant described previously, comprises a plurality of processing and/or assembly stations ST, for example, for carrying out operations on structures or components of motor vehicles. One or more electronic control and processing units PLC are associated to the assembly and/or processing stations ST, for control of at least one actuator AT and/or sensor S associated to the assembly and/or processing station ST. Finally, at least one human-machine-interface unit HMI is provided, configured for monitoring or controlling the assembly and/or processing stations ST through at least one electronic control and processing unit PLC.
Typically, the SCADA smart devices are implemented by means of one or more computers that are set outside the site in which the assembly plant is located, preferably in premises that are at a controlled temperature and relatively clean. Consequently, the aforesaid devices may even not be protected specifically from humidity, dust, temperature jumps, etc.
Instead, the fixed human-machine-interface units HMI are positioned in the proximity of the assembly stations and may be subject to critical working conditions as regards humidity, dust, and temperature jumps. Furthermore, in each plant a large number of fixed human-machine-interface units HMI are required, which contain a high level of built-in “intelligence” and entail high costs for their installation and maintenance.
With reference to FIG. 3, in a plant 1 of a known type the operator OP who wishes to intervene on a station ST must physically enter the area A in which the station ST is contained and, through the fixed human-machine-interface unit HMI associated to that A, can control the station ST.
Instead, the terminal SCADA is exclusively a monitoring terminal, from which the operator OP can observe the entire assembly line, but if an intervention is necessary, the operator OP must reach the fixed human-machine-interface unit HMI associated to the station ST to be controlled, and send directly, via the aforesaid fixed human-machine interface HMI, the command necessary for the station in question.
In particular, the fixed human-machine-interface units HMI are located near the stations ST to enable an operator OP to observe the effective status of the plant and see in real time the effects resulting from the modifications set via the command that he sends to the station. In this way, the operator OP is able to carry out, for example, an adjustment by varying the input parameters and noting the behaviour at output, thus carrying out a feedback control.
With the plants 1 of a known type the operator OP has only two possibilities for monitoring a given station ST, i.e., monitoring through the terminal SCADA or physically entering the associated control area A and querying the fixed human-machine-interface unit HMI on the status of the station ST.